1. Field of the Invention
The present invention relates generally to a two-way communication system and, more particularly, to a means which permits binary signals to be exchanged between devices through a single communication port, or pin.
2. Description of the Prior Art
When a pair of devices (e.g. such as a sensor and a programmable logic controller (PLC), two microprocessors, two sensors, or any two devices with input and output capability) need to communicate with each other, the standard method for permitting this two-way communication is to connect an output pin of the first device with an input pin of the second device and connect an output pin of the second device within an input pin of the first device. Binary information is then transmitted from the first device to the second device through one pair of communication ports, or pins, and binary information is transmitted from the second device to the first device through a separate pair of communication ports, or pins. Another method which permits two-way communication between devices utilizes time division multiplexing, wherein one device occupies each pin half of the time and the other device occupies each pin during the remaining time period. This multiplexing method does not permit either of the devices to provide a continuously valid output. This method and other known methods require additional input pins and circuitry to synchronize the output disable timing of one circuit with the input signal coming in from the other circuit. An input circuit that accepts the output from a bi-directional pin also requires a dedicated timing control function in order to read the desired output only when it is valid.
It would therefore be beneficial if a means is provided to permit two devices to communicate with each other through a single pin, or communication port, simultaneously without the signals from one device interfering with the signals from the other. This would be an improvement over known devices in which the output signal from a first device would corrupt the input signal coming from a second device to the first device.